Process for grinding and polishing lenses



A. C. ROBERTSON AND F. VOLK. PROCESS FOR GRINDING AN'D POLISHING LENSES. APPLICATION FILED APR. 15. I916. RENEWED 001. 22, I919.

Patented June 15,1920.

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A. C. ROBERTSON AND F. VOLK. PROCESS FOR GRINDINQAND POLISHING LENSES. APPLICATIONHLED APR. l5. i9l6. RENEWED OCT. 22. 1919.

Patented June 15, 1920.

5 SHEETS-SHEET 2.

A. C. ROBERTSON AND F. VOLK. PROCESS FOR GRINDING AND POLISHING LENSES- APPLICATION FILED APR-15'. I916. RENEWED OCT. 22. 1919. 0

1,343,522. Patented June 15, 1920.

5 SHEETS-SHEET 3- I 01 ll ll I A. C. ROBERTSON AND F. VOLK- PROCESS FOR GRINDING AND POLISHING LENSES. APPLICATION FILED APR- :5. I916. RENEWED 001,. 22. I9l9- 1,343,522.

Patented J um 15, 1920.

5 SHEETSfSHEET 4.

A. C. ROBERTSON AND F. VOLK- PROCESS FOR GRINDING AND POLISHING LENSES. APPLICATION FILED APR. I5. I916- RENEWED OCT. 22 1919- 1,343,522, Patented June 15, 1920.

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UNITED vfsmrs s -PMsurr- OFFICE.

I ALEXANDER corLANn nonnnrson, or NonTH SYDNEY, AND FRANK VOLK, or

' nNrIELn, Nnw sOUTH WALES, AUSTRALIA, ASSIGNORS To NIVERSAL GRIND- INe MACHINE oomrANY, or RENO, Nirvana, A CORPORATION OF NEVADA.

:Pnocnss FOB GRINDING AND POLISHING- LnNsns.

I Specification oil Letters Patent.

Patented June 15, 1920.

Application filed A rn s, 1916, Serial-NO. 91,357. Renewed Uctober 2a, 1919. semino. saaioo To all whom it may concern:

Be it known t at we, ALEXANDER "Cor- LAND RoRnRTsoN and FRANK VoLH, subjects of the King of Great Britain and Ireland, residing at 59 Walker street, North Sydney, New South Wales, Australia and Liverpool street, Enfield, New South Wales, Australia, respectively, have invented certain new and useful Improvements in Processes "for Grinding and Polishing Lenses, of which the following is a specification. v This invention consists in a process for grinding and polishing lenses, in which the required surfaces are ground and finlshed automatically to predetermined measure ments by rotary rubbing contact (and .111 certain cases by linear rubbing contact) between two opposed lens blanks or between a lens blank and a self forming opposed grinding surface.

In previous attempts to devise a means for producing-lenses automatically by ro tating two blanks in grinding contact, the one against the other, no success was at tained, for the reason that it was believed to be necessary to oscillate the spindle which carries the convexing member about'a' center at or about the center of revolution" of the required lens while the opposed blanks were kiefpt in motion. The knownprocess was in e ect a simple rindmg process, in which,

I during the grin ing, the convexing member was oscillated to and fro on a center on the radius of curvature of the required lens, while an opposed diskwas maintained in rinding contact with its surface. It is now established that neither convex nor concave sections of redetermined radius can be pro duced by t at process whether both disks be of glass, or one of glass and-the other of abradant substance.

The invention includes the production of spherical, spheroidal, cylindrical, toroidal, parabolic, and hyperbolic lenses; and also the production of piano and conical lens surfaces; and it is effectively carried out in a machine constructed as hereinafter described.

The blanks V pebble) disks of app oprlate diameter and thickness, and grinding anrhpclishing is as fected in amachine in which} two such blanks, or, in certain cases hereinafter deconsist I f glass (or natural fined, one such blank with a grinding or T polishing disk which automatically forms 1ts surface 1n the grinding operation, are

carried on spindles and are rotated in grind- 111% contact with each other. i

he two chucks or face plates which carry and the blank. (or grinder substance) held thereon is herein designated the negative.

The positive spindle is journaled in a carrier which is adjustable laterally in the machine frame in one plane about a pivot support, and this positive carrier is-associated 1 with mechanism by which oscillatory mo- .tion through any degree of arc may be applied to it when necessary; itmay also be locked in the machine frame in any certain angular position about said pivot. The positive spindle is capable of endwise adjustment in its journals in the positive carrier but during grinding operations its position is set'so that it'is not slidable axially'in its journals though it may be rotatedvtheref Means are also provided for bodily moving this spindle transversely of the,

plane in which its carrier is angularly ad- I j ustable in relation to the negative spindle.

In'most cases the positive blank is circular, but it is not necessarily circular.v 'In the case of toroidal and cylindrical lenses it I is'usually rectangular. The negative blank may in most cases be of any shape. For

brevity however these blanks whether of glass or abradant material, as for instance emery, are referred to. as disks, butit is to be understood that it is not therefore suggested that they shouldnecessarily be circular in section. 1 7

In this specification brevity of-de- A .sci-iption the normalposition of the spindles when; in alinement with each other is regarded and referred to as a vertical positiong-though it is obvious thattheir actual position relative to horizon is quite immaterial so long astheirpositions are correct I in-relation to eachxother. Any reference to theverticality or horizontality of any part must therefore'be read-on the assumption that the machine is erected and worked with its frame standing in a vertical positlon, as shown in the drawings.

The term grinding 1s to be construed so as to include polishing which is in effect a continuation of. the grinding proper, using lap the rotational axis of the opposing disk a predetermined extent when any section flatter than a hemisphere is being produced, and further observing that the positive blank is angularly adjusted to the plane of rotation of the negative disk about a point at which the center of curvature of the finished convex lens will be located at the completion of the grinding operation.

To obviate overgrinding, the axial feed of the negative blank is, inevery case of curved surface work, limited by a stop which prevents further feed and consequent unnecessary reduction of thickness of the lens and modification of its curvature aftera prede.

termined correct surface has been attained,

and in the case of plano surfaces is similarly limited after the required plano surface has been attained.

- Surfaces of modified spherical or indeterminate sections are obtainable when the setting of the negative blank is displaced angularly or laterally relative to the positive blank from; the normal position for s heri'cal grinding, or when the angularpos tion ofthe positive spindle is similarly changed, or. when ,overfeed is permitted to occur so that thene'gative blan grinds the positive blank deeper than thejpoint (center 'of curvature) about which the an ar position of thepositive spindle is fidJllStBd.

In conducting the grinding of two glass blanks, the positive and the negative surfaces produced on the opposing blanks are in certain cases exactly counterparts the one of the other. The intersection of the rotationalaxes (producedlof the o posing disks is on the radius'of curvature o the finished convex lens.v

In the ada roduction o cylindrical, toroidal, hyperbelie, parabolic, and other non-spherical sections, that essential feature 0f', the invention is retained.-

It is practicable by this process to grind tation of our process to theand polish lenses of very long focus; this indeed was not attempted to be done in the knownprocess in which the'positive plank was oscillated across the negative blank about a center always distant from the determined center of curvature of the finished lens, and limited necessarily by the dimensions of the grinding machine. In our machine any length of focus may be attained ranging from hemispheres to infinity.

It is entlrely practicable to substitute an emery or other abrasive disk for one of the glass blanks, subject to observance of certain operative conditions hereinafter described. In practice, however, it will be preferable-almost invariably to grind and polish two glass blanks one against the other, and our process is described herein on the assimptlon that two such glass blanks are so use For, the repolishing of existing lenses a cup chuck charged with polishing medium as a polishing pad, is set up on the negative 1 spindle head, with the lens on the positive chuck and the spindles set as for grinding that particular lens; the polishing operation is then conducted as if the lens and the pad were two blanks in process of grinding. A

perfect repolishing without any distortion of the original curvature is thus obtained.

In the accompanying drawings Figure is-a perspective View of the ma f chine;

Fig. 2 front elevational view bf the same; Fig. 3 transverse vertical section Fig. 4 is a sectional plan on line 4-4 ing with Fig. 4; i 6 is a fragment the eed'limit adj uster; Fig. 7 is a fragment vertical section fragment elevational view correspprn perspective 'view of through one rif the blank carriers or chucks on one of the spindle heads;

8 1s a detail section of the lower spin e showing a cup chuck mountedon the head thereof.

Fig. 9.is an elevational view of an angle jig fitted to the negative chuck for holding prism blanks;

F'gs. 10 to 12 are diagrammatic views explanatory of the procedure in setting up the machine to grind counterpart spherical lenses to a predetermined curvature, and Fig. 13 a slmilar view explanatory of the polishing of a finished lens or the repolishin of an old lens; 7

igs. let and 15 are diagrammatic views explanatory of the setting of the spindles for the grinding of hyperbolic lenses, Fig.

15 being taken in side elevation, and

" Fig. 16'is' a similar viewexplanatory of the regrinding (correcting.) of a spherical lens to produce a lens of hyperbolic section;

Eig. 17 indicates the setting for the purpose of modifyingv counterpart spherical forms to obtain parabolas;

Fig. 18 shows the setting up of the machine for the production ofconca've spheroid Fig.- 20 is a diagrammatic representation of the setting of the machine for the grind in of toroidal sections.

lg. 21 illustrates two perspective views of counterpart convex and concave cylindricallenses such as are produced in the first I grinding along the major axis of the blanks as described with reference to Fig. 20; and Fig. 22 shows two similar views of the torodial lenses which result from regrinding the cylindricals (Fig. 21) along the minor axis as described with reference to Fig. 21.

Fig. 23 explains the setting up of the machine for the production of a, convex cylindrical surface.

Fig. 24 shows the convex cylindrical blank and the grinding disk or plate as they appear in section through the progress of or at the completion of this operation.

Fig. 25 illustrates'the setting up of the machine for grinding and polishing plano surfaces; f

Fig. 26 is a similar view explanatory of the setting for the grinding of conical forms. I Fig. 27 shows a blank set up on the negative chuck jig and an abradant disk on the positive chuck.

Fig. 28 shows the position of the parts at the conclusion of the operation illustrated in Fig. 27. i

Fig. 29 is a diagrammatic-view explanatoryof the grindin of facets'on a sphere or other regular solid body.

7 It is practicable to use a negative or a positive disk of emery or other abradant material to grind a glass blank in any of the ,casesdescribed, .but in order to insure cor- 'rec'tness of form in a glass lens so ground by means of an abradant disk, it must be observed'that the abradant disk shall be of' such composition that its rate of wear is approximately identical with the rate of reduction of the glass disk; otherwise the curve produced on the glass will not the designed curve. The machine is set up-by adjusting the positions of the spindle and disk surfaces to certain ga es, having regard to the type, diameter, an curvature of the lens or lenses to be produced.

The spindles are'arranged'in vertical relation on the machine housing or frame 40, which takes'the form of a vertical face plate having a horizontal pivot 42 fixed in it, upon which pivot the positive spindle carrier 43 is mounted. This carrier has two journal hearings in lugs 45' and 49 located the chuck 50 in Fig. 3.

, .tive spindle.

some distance apart, inwhich bearings the positive spindle 46 is rotatable by means of a flexible shaft connected to the universal joint 47- at the head of said spindle, or otherwise. Intermediate of the journal bearings the spindle 46 is screw threaded, and on this which the lens blank is mounted in pitch or other setting. The detail of this face plate or chuck is shown'in Fig. 7, and the detail of a cup chuck on the lower spindle is shown in Fig. 8. The face plate 51 is'constructed with a dovetail foot 52' which engages the dovetail end 53 on a socket 54 which is fitted on the lowerend of the spindle 46 and secured by a pinching screw 55 or otherwise. The face plate 51 in Fig. 7 corresponds with The sleeve 56 is tapped and runs on the threaded exterior of the socket 54 and takes over the foot 52 of the face plate 51, .so that when it is screwed down, the faceplate 51 will be tightly held on the dovetail mounting, and the surfaceof the face plate will be brought exactly square with the axis of the spindle 46. A collar 57 with pinching screw takes against the end of the underside of the bushing of the upper journal bearing 45 and enables the spindle 46 to be set up so that the face plate will be immovable axiall upward but rotatably free. By traversing the sleeve 48 on the screwed portion of the spindle and adjust-' ing the collar 57, the spindle is set so that the blank on the positive chuck .50 may be fixed with and locked against vertical movement. The center pivot 42 is socketed to carry the tan of a knife edge gage 58 the edge of whic is central to the socket, so that when the tan 59 isset in any position in "the socket the ife edge will still be in one line wit the axis of the pivot 42. This gage is to b used only when setting up the machine for the grinding operation. The tang 59 is preferably made rectangular, and the socket of corresponding rectangular dimensions and'a neat fit for the tang.

The positive spindle journal bearings 45 and 49 are connected by a frame member 60 which is slidable transversely of the frame 40-on brackets 61 and 62 projectingf'rom the carrier 43, and can be set transversely out of alinement with the journal bearings of the negative spindle b slidin the frame member 60 out upon t e brac ets 61 and 62 as far as may be necessary, their transverse displacement from normal center being indicated by a pointer 63 working over a scale 64. At the O on this scale the positive spindle is in axial alinement with the nega- The position of the journal bearings 45 and 49' is set by means of pinchin screws 65.

I he upper part" of the housing '40 is open as shown at 66, and a sector 67 forms a guide quadrant for a clamp runner 68 with clamping screw 69. The quadrant is graduated preferably in degrees of arc, and a pointer 7 0 indicates the angular position of the carrier on this scale. A suitable micrometer adjustment may be fitted to the clamp 68 to facilitate fine setting. I

An arm 71 is offset at right angles from the carrier 43 at its pivotal center, and this arm carries a slider 72 with upstanding square edge 73. The slider has a straight edge-7 4 which works over a scale 7 5 on the arm 71 to indicate lens diameters; The figuring on this scale is'to quarter diameters, that is to say,.for instance, the figure 2 while indicating a 2 diameter lens is situate only 1} from the axial center 42. When the edge 74 reads at 0, the square edge 73 is in alinement with the pivot axis 42. This slider is set by a pinching screw 76, and when it is set to any particular measure, the edge 73 of the square is located one quarter of the indicated measure from the center 42.

The carrier 43 has a vertical extension arm 7 7 below the center 42. This arm is the means by which, when necessary, oscillating motion is applied to the carrier 43 about the center 42 by means of a connecting rod 78 with sleeve length adjuster 79 and adjustable driver 80, turned by a spur wheel 81.

the drawing. Drive is applied to either of these wheels 81 and 82 by a flexible shaftor otherwise.

A transverse slot 83 with guide flanges 84 accommodates the slide 85 on which the negative spindle is supported. The slide is rabbeted as shown, and a set screw 86 is pro-' vided to lock it at any certain position in the slot. The. slide supports a carrier arm 87 fitted wiiii a pivot 88 which is in axial aline'-- ment with the housing pivot 42 when the slide is in the central position. The axes of the pivots 42 and 88 are always in the same horizontal plane. Upon the p1vot 88 is hung the stage 89 onwhich the negative journalbearings 90 and 91 are mounted, and this stage may be swung aboutthe pivot 88 and locked in vertical or angular position-on the slide by means of a clampscrew 92 working in a sector slot 93, a pointer 94 and quadrant" scale 95 markedin degrees of are being provided to indicate its position, and a micrometer attachment of convenient design (not shown) being also fitted to facilitate fine adjustment. In the pivot 88 is an axial socket 96 adapted to carry the tang of a knife edge :with said socket. This knife edge is used only when setting up the machine for the grinding operation. 98 is a pin on the slide 85 adapted to take the end ofthe adjustable connecting rod 99 which is driven by the adjustable crank. pin 100'which is turned by the spur wheel 82. ()n the carrier 89 is a crank pin 101 adapted to take the end of an adjustable connecting rod 78 which is adaptedto bedriven by the crank pin 80, which crank pin as before stated, serves also when necessary to apply oscillating motion to the positive carrier 43-. i

The socket hole 96 extends clear through the pivot 88 and is adapted to carry the tive spindle when both spindles are in the central vertical position shown in Figs. 1 and 3. A face plate 103"or chuck is mounted on the top end of the negative spindle 102, with parts identical with those used for fixing the face plate or chuck 50 on the bottom end of the positive spindle 46. These parts being designated 51', 52, 53, 54' and 56. in Fig. 8." 1 J Belowi'ts upper bearing a tapped sleeve 104 runs on the screwed part of the lower spindle 102. The part ofthe spindle above said thread and, the part below it are slidable axially within'the bearings 90 and 91" respectively so that the spindle may be rotated andat the same time slid axially in said bushes. The limit of its upward movement is set by adjusting the sleeve 104 which acts as a stop when it meets the under end to it to cause rotation of the chuck or face plate 103 in the same direction as the chuck or face plate 50, or oppositely. Above the universal joint is a running collar 106 with trunnion pins 107 which work in a'slotted lever 108 fulcrum'ed on abracket Mm 109 depending from the stage 89. A weight 110 acts through the lever 108 to move the spindle 102 upward'when .it' is not restrained against upward movement by its stops, and

operates to maintain contact of the negative blank with the positive blank during grindg ing, thus feeding the negative toward the positive as the blanks are ground away. I

The limit stop' adjustment coacting with the milled flangeof the tapped sleeve 104, j

which effects the correct setting of the stop feed position of the negative spindle 102,

1 positive spindle is for certain purposes ca consists of a slider 112, traversable across the face of the stage 89 and fixable thereto by means of a jamming screw 113. A scale the gage position for a lens four inches in diameter, but the actual measurement-of the mark '4 from the mark 0 on the scale is only two inches, The movement of the pointer 115 across the scale 114 indicates the lateral position of the slider 1-12 on the stage 89 and the lateral displacenlllent of the negative spindle in relation to t e the slider 112 carries a pivot'117 on which a bell crank slotted adjusting lever 118 is hung. The adjusting arm 119 of this lever .118 moves over a degree sector scale 120 on the edge of the slider 112, and said arm. is fixable in any certain position by means of a wing nut 121 on a pinching bolt which works in a radial slot 122 in the slider. The.

movement of the slotted work arm after the slider 112 has been set is the correct adjustment for lower limit positionof the sleeve 104 so that it will contact with the journal bearing 90 and stop upward feed motion as soon asthe negative disk surface has. reached the horizontal plane of the pivots 42 and 88. v

It will be observed that the positive spindle may be set up at any angle between extreme angular working position (45) and 0 (vertical position) in the houslng, and that that spindle may be adjusted endwise in its bearings so' that the face of the blank whichit carries maybe in transverse alinement with the axis of the carrier pivot 42, or may come above or below that point of alinement if.so required. Also, that the pable of oscillating motion about the center 42 but is not capable of any reciprocating motion; Also that the negative spindle is so mounted that its vertical position in its journal bearings may be varied, the limit of this vertical movement controlled by a stop with hand setting, its angular p'os1- tion fixed about its carrier pivot 88, that it may be traversed horizontally of the housing, and that it may be oscillated about the pivot 88. g r

The face plate fitting shown in Fig: 9

pivot 42. A lug 116 projecting from consists of a jig table'128 movable about a hinge support 129 and fixable by two clamp screws 130 and 131, the angularity in grees being indicated by a, marked scale 132 on a quadrant 133 which passes across the normally horizontal surface of the face plate 51. v

To produce for example a spherical lens,

reference being had to Figs. 10 to 12, the

positive blank 134 is mounted on the chuck 50 and the positive spindle 46 adjusted by means of the collar 57 and sleeve 48 so that the point on the under surface of said blank which is to be the center of curvature of the lens about to be reduced is on the axis ofthepivot 42. his is effected by using the knife edge 58 as a gage. 46 is then fixed by the collar 57 and the sleeve 48 so that it is no longer movable axially in its journal bearings. The 'nega-' tive blank 135 is now mounted on the nega- The spindle tive chuck 103 and the negative spindle allowed to rise in its journal bearin s until the top surface of said blank touches the knife edge 97. The slider gage 112 is now .set over to the gage mark (lens diameter) on scale 114, and the pointer gage 119 is set to the same gage mark as the pointer 7 0 on thescale 67 6. one fourth the angle of curvature) thereby bringing the limit stop knuckle 126 is now slid laterally in its dovetail slide 136 to give clearance to allow the spindle 102 and the sleeve 104 to be slid downward. The squareedge gage 73 is now set over to the gage mark on its scale '95 knuckle 126 to a corresponding position.

75 indicating lens diameter, and then the positive carrier is'set over from the vertical,

about the center 42 one fourth the angle of curvature of the required convex lens-that is one fourth the number of degrees-contained between radii drawn to opposite points onathe periphery of the arc of curvature of the required lens surface. This done,

the positive'carrier. is fixed at that angle by tightening the screw 69. The slide 85 is now moved laterally until the knife edge I 111 contacts with the square'edge 73 (see Fig.

11) and the slide is then locked by the pinching screw'86. This lateral ad ustment of the negative spindle sets it over from the axialcenter 42 a distance which is the ratio of the angle of the positive spindle from the-verticalon an adjacent side equal to one fourth the diameter of the lens about-to be ground. The knife edge gages are now removed and the negativeblank allowed to move up and touch with the positive blank andstay in grinding contact withithy the action of the weight gear 108-110. Rotary motion is now applied to the spindles, clock wise to one and counterclockwise to the other, and abradant material is served to the grinding surfaces, and the grinding continued until the feed of the negative spindle is arrested by the contact of the sleeve 104 with the journal bearing 90, at which point I to 13 that the rotational axis of the negative blank 135 would if produced, intersect the axis of the positive spindle at a point which is the radial center of the curve of the lens (see F ig; 19), and it will be observed that it is necessary that the diameter of the blank 135 shall be equal to or greater than the diameter of the blank 134.

The process of modifying spherical lenses to produce parabolic lenses is suggested in Fig. 17. Having procured counterpart spherical convex and concave blanks 134 and 135, the same are set up on the positive and negative chucks respectively, with the center of curvature in alinement with the axis of the pivot 42, and with the positive and negative spindle axes both vertical and therefore in alinement, and then fixing the sleeve 104 to prevent upward movement of the negative spindle 102. The negative spindle can move backward against the reaction of the loading weight lever 108, and thus allow the negative blank 135 to ride back from the positive blank 134, but neither blank can be advanced toward the other one beyond the set point, which is the center of,

cated on the scale 95. Meantime both spin-- dles are maintained in rotation in opposite directions. The result of this operation is that the outer zone of each'of the sphericals is ground away, while neither is reduced at the center of curvature, and they are each ultimately brought to a section corresponding to a parabolic section, the dimensions of which are determined by the original dimensions of the spherical blanks and the range of the oscillating motion. It is important to note that this oscillating motion occurs about a center which coincides with the center of the complementary spherical blanks.

orizontal plane ofthe axis of the Fig. 18 indicates the operation of a process for modifying spherical sections so as to produce lenses of spheroidal or like elongated curved sections, that is lenses having a flatter section in one direction than in another direction at right angles thereto, the shorter section being identical with the original spherical section. This is effected by setting up the already ground counterpart spherical lenses precisely in the same manner as described with reference to Fig. 17, and applying rotary motion to the positive spindle and reciprocating motion to the slide 85, through the connecting rod 99 acting on the pin 98, the stroke of the crank 100 being in this case also adjusted having regard to the dimensions of the finished modified spherical section required. The positive spherical blank will act as a self forming tool to grind the negative spherical blank to spheroidsection. I

Figs. 20 and 21 refer to the grinding of cylindrical lenses. In. setting the machine for this purpose, a blank 134 is mounted on the positive chuck 5.0 and the positive spindle is set in its journal bearings so that the under face of the blank 134 is brought into contact with the knife gage 58, the tang of which is set in the axial socket in the carrier pivot 42, or is brought below said gage 58. The negative blank 135 being now mounted on the chuck 103, the negative spindle is permitted to rise until the opposed faces of the two blanks come into contact, and then the sleeve 104 is set on the negative spindle 102, to limit feed of the negative blank and arrest grinding as soon as counterpart curved surfaces are produced. The slide 85 is set centrally so that the pivots 42 and 88 are in exact axial alinement. The grinding operation 'consists in holding the positive blank 134 fixed,

and oscillating the stage '89 about the pivot 88 through an arc the length of which is determined with regard to the curvature required. The radius of the convex cylinder thus ground depends upon three factors: viz. (1) the distance of the fixed under surface of the positive blank below the pivot axis 42, (2) the length of the positive blank in the plane of the oscillating motion of the negative blank, and (3) the range of the j oscillatory movement of the -negative blank or grinder. All three of these adjustments must be determinedto enable the setting of the machine for the correct grinding automatically of cylindrical curves to a predetermined radius. Even if the under surface of the positive blank is set in alinement with the center pivot axis 42, about which axis the negative disk or grinder block oscillates, counterpart cylindrical forms are obtained having a radius of curvature located at a point on or above said axial center 42; inthis-case however, as grinding is continued, the radius shortens, until ultimately the positive blank is reduced to m'l at the oscillation center. Throughout the grinding, however, the counterpart cylinders obtained are true cylinders aftenthe grinding has progressed sufficiently far to bring thewhole area of the opposed sur-- faces into contact. It is necessary therefore to set the feed stop of the negative spindle to arrest further feed as soon as the grinding has produced the required radius of curve. 1

Convex cylinders are obtained by another method. lln this case (Fig. 23) the blanks are set face to face on. the plane of the axial centerof the pivot 42, the positive carrier is oscillated about the axis 42, its spindle beinglocked against any movement in its journal bearings, and the negative is rotated and at the same time reciprocated through a range which at each movement brings the center of each blank to or slightly past the edge of the other blank.

It is necessary to observe that other types of lenses are procured by a variation in the procedure for the grinding of cylindrical lenses.- For instance, if either blank be rotated during-the grinding operations already described for cylinders, a toroidal lens and a lens of modified spherical section are obtained. Cylindrical counterpart lenses- Fig. 21.) are convertible to toroidal lenses Fig.22) by a repetition of the cylindrical grinding process with the c lindrical blanks set on their chucks turne 90 from their original position thereon, and similarly the ,convex cylinder produced as described with reference to Fig. 23' is convertible to a convex toroidal lens.

Toroidal lenses may also be made. direct from flat blanks. In this case, referring to Fig. 26 (which as drawn refers to the grinding of cones), the blanks are mounted and the spindles set up in angular relation, as for roducingspherical lenses; the positive blan is rotated, andthe ne ative blankis reciproctrted (but not rotated horizontally,

and the positive spindle is set so that it cannot move axially in its journal bearings. The negative spindle is set with freedom to feed upward. A concave toroidal lens is thus obtained, while the positive blank is ground to a hyperbolic section. As in-other cases described, the measurements of the finished lenses depend upon a correct setting of positions of the spindles and the range of the reciprocating or oscillating move ment (if any) having regard to the diameter of the blanks bein operatedon. I

The grinding o cones is a simple operation, which consists in settin the positive spindle to the appropriate ang e, and having mounted the blanks on the chucks, maintainthe edge of the positive passes up to or slightly over the center of the negative disk on each reciprocation.

Heretofore it has been attempted to grinpi I 'is therefore rendered incapable of producing a true face on the blank. According to our invention two optically true plano surfaces are obtained simultaneously by grinding two blanks together while both are rotating and one is reciprocatedacross the other,'but always so that it does not at any part of it substantially overlap the axis of rotation of said other blank. This operation may be best'understood by reference to Fig. 25in which the negative blank 135 is shown at the extreme end of its stroke withits edge just overlapping the axis of rotation of the positive blank 134. The operation for the grinding of prisms and bevel edges is mechanically identical, a convenient device for carrymg the prism or bevjel blanks at the required angle on the negative chuck being shown in Figs. 27' and 28.

In another method of grinding hyperbola lenses, the slide 60'is moved to set the ositive spindle 46 over transversely out o the plane in which the negative spin le performs its various motions. This i shown in the diagrammatic view (Fig. 15). The angular position of the positive spindle is set as for spheres, then the'positive spindle.

is moved over 'as above stated and both spindles are rotated, with freedom to the negatlve to slide in ts journal bearings. A I

convex and a concave hyperbola are thus obtained, but they are not counterparts.

Their measurements depend on the angularity and eccentricity of the positive disk in relation to the negative disk.

Fig. 16 is a sectional diagram explanatory of the grinding of hyperbolas and parabolas from counterpart spherical blanks. During this operation both blanks are rotated, their relative axial positions and feed limits being adjusted with relation to the dimensions andproportions of the sections required. The

negative spindle is set over from the position it would occupy if these blanks were to be further gI ound as sphericals", by-moving the slide 8'5fl'aterally across the machine so as to bring the point of intersection of the negative spindle axis lower down on the positive spindle for hyperbolas and higherupthereon for parabolas. 'Hyperbolas are also obtained by increasing the angular position of the positivespindle and retaining the nega- I tive spindle in the position set for the-original sphericals. The positive spindle is locked amount of lateral displacement of the negative spindle from the normal setting to produce the spherical blanks which are required to be converted are both factors which affect the proportions of the curves produced in this operation. Convexes and concaves are produced in this manner but they are not counterparts the one of the other.

For grinding facets on spherical orot-her non-concave solid forms (see Fig. 29) the blank is mounted on the positive chuck and the positive spindle is set at an angle (relative to axis of blank) of the required facet. The negative chuck carries a grinding surface and it is rotated and reciprocated transversely of its axis. As each facet is completed the positive spindle is unlocked and turned to expose the surface on which the next facet is to be ground, and then locked again, and the grinding of the several facets to complete a belt of facets is thus successively effected. After each belt of facets is completed, the angle of the positive spindle is reset for the next belt of facets, and the same series of operations repeated. A perfectly symmetrical system of facets covering the whole or any part of the blank is thus produced. The negative spindle is free to slide axially during these operations, but as in all other cases the stop operates to limit the feed and therefore to prevent overgrinding;

Where in this specification it is provided that the periphery or edge of'one blank must overlap the axis of the opposed blank, it-is to be understood that the necessary condition is satisfied when such periphery intersects such axis, but it is impracticable to attain precise accuracy in this particularand it is quite unnecessary to do so. It sufiices to set the periphery of one blank very slightly overlapping the axis of the other blank, and

this can be done readily. Care must always be exercised when observance ofthis condition is called for, to insure that the periphery of either blank does at least intersect the center of the'opposing blank throughout the grindingoperation.

We would have it understood that the descriptions of operations herein particularly blank is one which at the conclusion of the operation is on the center of the finished convex lens, and always feed is obtained by moving the negative blank (or grinder) axially upward. Whether the blanks are to be rotated, oscillated, or reciprocated, is de: termined by the type of lens to be produced. In all cases the angular and rectilinear motions occur in thesame plane (though in one exceptional casehyperbolas, Fig. 15the rotary movements are in parallel planes), and the axial line of the negative spindle if produced intersects the axial line of the positive s indle.

In ig. 19 the line w is the normal vertical, which is" the common axis in which both spindles may be set. The center of the lens surface a is always located on this line. 3 is the surfaceof the negative blank, and z the surface of the opposed positive blank at the commencement of the grinding operation for sphericals. X is the axis of the negative spindle, and Y is the axis of the positive spindle. The axis x cuts the axis Y at the center of the lens surface 0 on the surface .2. 73 is the square edge (see Figs. 4: and 5) set over from the center of the lens surface 2) one fourth the required lens diameter, and 111 is the, negative carrier knife gage which contacts with the square edge 7 3 and sets the negative carrier over that distance laterally from the center of the lens surface '1) which is the ratio (w) of the angle m on the adjacent side a. The angle on is equal to the angle 0, and the side n is one fourth the lens diameter. a is the angle of curvature of the required lens,

angle 0 so that the adjacent side S, which is a line bisecting the angle 6, is vertical to the plane of rotation y of the ne ative blank. The line S is necessarily in alinement with the negative axis X, and it cuts the positive axial line Y at the point T which is the radius of curvature of the finished lens surface U.

What we claim as our invention and desire to secure by Letters Patent is 1. The process of producing lenses which consists in grinding the lens blanks with abradant disks Whose rate of wear is substantially the same as the rate of Wear of the lens blanks while maintaining a fixed angular relation between the blanks and disks.

2. The process of producing lenses which consists in grinding two blanks of substantially the same rate of wear one against the other with, their axis fixedly inclined to each other.

3. The process of producing lenses, which consists in grinding two blanks at substantially the same rate of wear, one against the other while the-axes of said blanks are fixed in angular relation.

4. The process of grinding lenses which consists in grinding two blanks of substantially the same rate of wear one against the otherwith their focal axes intersecting, and the periphery of each said blank overlapping the axis of the other blank. 5. The process of producing lenses which consists in rotating a lens blank in grinding engagement with a rotating abradant" disk whose rate of wear is substantially the same asthat of the blank and whose rotational axis is fixedly inclined to rotational axis of the blank, and progressively feed-,7 to each other as the lens blank.

ing the disk and'blank grinding proceeds.

7. The process of producing lenses which consists in grinding two counter-part lens blanks, one against the other with their focal axes fixedly intersecting, feeding one of the blanks toward the other as the grinding proceeds, and interrupting the feeding operation at a predetermined point in the grinding operatlon.

8. The process of producing lenses by grinding two lens blanks of the same rates of wear, the one against the other, which consists in mounting the blanks with their axes inclined to each other and intersecting at a point on the radius of curvature of one of the finished lenses, and rotating the blanks in grinding engagement with each other.

9. The process of producing lenses which consists in rotating two counter-part lens blanks, one against the other, inplanes inclined to each other, and with the edgeof each over-lapping the axial center of the opposed blank.

10. The process of producing lenses which consists in rotating two counter-part lens blanks, one against the other in planes fixedly inclined to each other and with the edge of each blank over-lappin the axial center of the o posed blank and eeding one blagk toward t e other as the grinding procee s.

11. The process of producing spherical lenses which consists in rotatin about their axes two counter-part lens lanks, one against the other, in planes fixedly inclined to each other and with the edge of each blank over-lapping the axial center of the other, feeding the concave lens blank toward the convex blank as the (grinding proceeds, andinterrupting the fee when the grinding reaches the axial center of the convex 12. The process of reducing counterpart lenses with spherical surfaces which consists in mounting two counter part lens blanks in planes fixedly inclined to each other and with their axes intersecting at the center of the revolution of the convex lens and with the edge of each blank overlapping the axial center of the other blank,

rotating both blanks in grinding engagement with each other, feeding the concave blank toward the convex blank as the grinding proceeds and interrupting the feed when the axial center of the convex lens is reached. o

In testimony whereof we have afiixed our signatures in presence of two witnesses.

' ALEXANDER GOPLAND ROBERTSON.

FRANK VOLK- Witnesses:

H. C. Cxmnnnn,

W. I. DAVIS. 

